The present invention relates generally to high-speed data communication systems, and specifically to Digital Subscriber Line systems.
Digital Subscriber Line (DSL) is a modem technology that enables broadband digital data to be transmitted over twisted-pair wire, which is the type of infrastructure that links most home and small business subscribers to their telephone service providers. DSL modems enable users to access digital networks at speeds tens to hundreds of times faster than current analog modems and basic ISDN service. DSL thus opens the Most critical bottleneck in local-loop access to high-speed networks, such as Asynchronous Transfer Mode (ATM) and Internet Protocol (IP) networks, without requiring major investments in new infrastructure. A range of DSL standards have been defined, known generically as xe2x80x9cxDSL,xe2x80x9d wherein the various standards have different data rates and other associated features but share common principles of operation.
DSL subscribers are connected to high-speed networks through Digital Subscriber Line Access Multiplexer (DSLAM) systems. Because of the high cost of network bandwidth, a single DSLAM must typically be designed to serve between 100 and 1000 subscribers and to concentrate their traffic through one or a few high-speed network trunks. The need to serve such a large and potentially variable number of subscribers in the one DSLAM has led to the development of xe2x80x9cmulti-shelfxe2x80x9d access architectures. In the physical implementation of such systems, each of the shelves holds a switching unit and a group of line cards. Each line card has a number of ports that serve network subscribers. Each switching unit links the shelf to the network trunk (either directly or through the switching unit of another shelf) and multiplexes the network connection among the line cards.
In order to reduce maintenance costs, DSLAM systems are typically configured so that, insofar as possible, management and maintenance activities are carried out using a remote management station. The object of this configuration is to minimize the number of service calls that a maintenance engineer or technician must make to the site of the DSLAM. Typically, the management station communicates xe2x80x9cin-bandxe2x80x9d with the switching units, i.e., via the high-speed network. Alternatively, the management station may communicate with the master unit via an xe2x80x9cout-of-bandxe2x80x9d network, such as an Ethernet network, or by a point-to-point (PPP) dial-up connection.
In some configurations, the remote management station communicates with the elements of the DSLAM using IP addressing and messages over a public network. With the explosive growth of the Internet, however, IP addresses are becoming scarce. The Internet Engineering Task Force (IETF) has proposed methods of Network Address Translation (NAT) for reducing the number of IP addresses used in public networks. These methods are described in detail in IETF Request for Comments (RFC) 2631, which is incorporated herein by reference and is available at www.rfc-editor.org/rfcsearch.html.
It is an object of some aspects of the present invention to provide an improved management network for a high-speed network access multiplexing system, and particularly for a multi-shelf access system.
It is another object of some aspects of the present invention to provide an Internet Protocol (IP) management network for a multi-shelf access system that uses a minimal number of IP addresses.
In preferred embodiments of the present invention, a network access multiplexing system comprises multiple shelves, each shelf comprising a switching unit, linked to the network, and one or more line cards, having ports that serve respective network subscribers. The shelves comprise a master shelf, having a master switching unit connected to the network, and a plurality of slave shelves, having slave switching units linked to the network through the master switching unit. The master shelf serves as a gateway for an IP-based management network, through which a remote management station communicates with the master and slave shelves to perform configuration and maintenance functions.
The management station communicates with the shelves using a transport-layer protocol, such as the User Datagram Protocol (UDP), with a different session-layer port, such as a UDP port, assigned to each of the shelves. In other words, the UDP port is used as a hardware address, rather than as a session-layer port for a given presentation-layer protocol as is known in the art, so that only one network-layer (IP) address per trunk connection to the master shelf is required in order for the management network to address all of the shelves in the multiplexing system. Internally, the master shelf maps the UDP ports to local network-layer addresses, preferably IP addresses, of the slave shelves. The mapping is carried out automatically, based on the topology of the multi-shelf system. Thus, the master shelf determine al of the UDP ports and corresponding internal IP addresses autonomously, without the need for programming of Network Address Translation (NAT) data as in systems known in the art. The slave shelves similarly determine their own internal IP addresses.
There is therefore provided, in accordance with a preferred embodiment of the present invention, communication access apparatus, including:
a master shelf, including a master switching unit linked to communicate with a high-speed network;
a plurality of slave shelves arranged in a given system topology with respect to the master shelf, each of the slave shelves including ports configured to serve network subscribers, and further including a slave switching unit, coupled to communicate with the master switching unit and to multiplex among the ports so as to provide the subscribers with access to the high-speed network, and to receive from the master shelf management messages that are addressed to an internal network-layer address that is determined uniquely for each of the slave shelves based on the topology; and
a management station, coupled to convey the management messages to the master shelf over a management network in which at least some of the slave shelves share a common external network-layer address by mapping the internal network-layer address of each of the shelves to a respective transport-layer address.
In a preferred embodiment, the master shelf and the plurality of slave shelves belong to a Digital Subscriber Line Access Multiplexing (DSLTM) system. Preferably, the high-speed network includes an Asynchronous Transfer Mode (ATM) network, wherein the master and slave switching units communicate over ATM lines. Further preferably, the management network includes an Internet Protocol (IP) network, which is operative over the ATM lines using an IP over ATM protocol. Most preferably, the external network-layer address includes a single IP address that is common to the master shelf and to all of the slave shelves.
Additionally or alternatively, the respective transport-layer address to which the management station maps the internal network-layer address includes a session-layer port. Preferably, the session-layer port includes a User Datagram Protocol (UDP) port. Further preferably, the management station is adapted to map each internal network-layer address of each of the shelves to multiple different session-layer ports, depending on a presentation-layer protocol used in the management messages. Most preferably, the internal network-layer address includes an internal IP address, and the master switching unit is adapted to map the session-layer port in the management messages to the internal IP address.
Preferably, the master switching unit is adapted to analyze the system topology and to assign the internal network-layer address of each of the slave shelves automatically responsive to the analyzed topology. Most preferably, the master switching unit is further adapted to determine the mapping of the internal network-layer address of each of the shelves to the respective transport-layer address automatically responsive to the analyzed topology. Additionally or alternatively each of the slave shelves is adapted to determine its respective position in the topology and to recognize its internal network-layer address responsive to its determined position. In a preferred embodiment, the topology includes a plurality of daisy chains, over which the slave switching units are coupled to communicate with the master switching unit, and the internal network-layer address of each of the slave shelves is determined uniquely by an identifying number of the chain in which the shelf is located and a position of the shelf in the chain.
There is also provided, in accordance with a preferred embodiment of the present invention, a method for providing communication access, including:
linking a master switching unit on a master shelf to communicate with a high-speed network;
arranging a plurality of slave shelves in a given system topology with respect to the master shelf, so that a slave switching unit on each slave shelf communicates with the master switching unit and multiplexes among subscriber ports on the slave shelf so as to provide the subscribers with access to the high-speed network;
assigning to each slave shelf a unique internal network-layer address based on the topology, for receiving management instructions from the master switching unit;
conveying the management instructions from a management station to the master shelf over a management network in which at least some of the slave shelves share a common external network-layer address, by mapping the internal network-layer address of each of the shelves to a respective transport-layer address.
The present invention will be more fully understood from the following detailed description of the preferred embodiments thereof, taken together with the drawings in which: